DK2467502T3

DK2467502T3 - Process for producing leather pellets

Info

Publication number: DK2467502T3
Application number: DK10737317.7T
Authority: DK
Inventors: Thomas Christof Bader
Original assignee: Bader Gmbh & Co Kg
Priority date: 2009-08-18
Filing date: 2010-07-26
Publication date: 2016-04-04
Also published as: US20120133071A1; EP2467502A2; US8623249B2; EP2467502B1; WO2011020680A2; ES2561432T3; HK1167165A1; JP5707403B2; DE102009037792A1; WO2011020680A3; CN102471808A; JP2013502470A; PL2467502T3; CN102471808B

Description

The invention relates to a method for producing leather pellets, in which shavings are obtained as a waste product in leather production and the shavings are comminuted to a ground leather stock containing leather fibres.

In the course of industrial leather production, the hides are shaved, i.e. planed off on the reverse by means of a spiral knife cylinder to a uniform thickness, e.g. 1.5 mm, in one of the process steps. The planed-off material is the so-called shavings, which are obtained in an amount of about 33 % of the hide weight. Depending on the tanning method, the shavings have been used hitherto either for leather fiber production (chrome shavings) or for composting (chrome-free shavings), and taken to waste dumps.

In a known method of the type specified at the outset (WO 2007/121497 A), leather waste in the form of shavings is comminuted to a ground leather stock containing leather fibres and sent in this form to further processing.

In all of these cases, the future routes for utilization and disposal of the leather waste are uncertain and associated with costs.

On the basis of this, the object of the present invention is to develop a method for utilizing shavings obtained in leather production.

To achieve the object, the combination of features described in claim 1 is proposed. Advantageous embodiments and further developments of the invention emerge from the dependent claims.

The invention is based above all on the concept that the shavings can be used appropriately and further processed industrially if it is first processed to an intermediate product. This intermediate product acquires the form of leather pellets which are produced by the following steps in the method according to the invention: Shavings are obtained as a waste product in leather production; the shavings are comminuted to a ground leather stock containing leather fibers; the comminuted shavings are pressed to leather pellets; and the leather pellets are dried to a residual moisture content of a maximum of 30 wt.%. In this context, the shavings can be obtained both in a chrome tanning and in a tanning with glutardialdehyde.

The shavings are expediently first comminuted to a fiber or particle size of about 0.5 mm by fine grinding. Pressing of the pellets can be carried out in a conventional pelleting press. Depending on the requirements of the subsequent further processing processes, the pressed leather pellets can be dried to a residual moisture content of 5 -30 wt.%. For processing in some machine types, a lower residual moisture content is necessary, since these machines would otherwise be exposed to the risk of corrosion by the moisture, while other machine types are less sensitive in this respect.

In contrast to the ground leather stock, the leather pellets are easy to handle as bulk goods, and when packed have a storage stability of months or even years.

The pressed leather pellets are an intermediate product which can be further processed in various ways. In a method according to the invention for further processing of the leather pellets, the pellets are mixed with a thermoplastic polymer material in the ratio of about 10-95 % and bonded into compound granules of leather fibers and polymer material. This is carried out in an extruding machine, to which the polymer material and the leather pellets are fed as a premix or separately. During the extruding operation, the mixture of leather pellets and polymer material is homogenized, so that the compound granules are a matrix of polymer material with embedded leather fibers. During the production of the compound granules, a dyestuff can be added to the polymer material, which is conventionally colorless per se, in order to give the granules a desired color. It is also possible in principle for the ground stock to be already colored with conventional leather dyestuffs during production of the leather pellets. However, it has been found that the color stability cannot always be controlled with the necessary precision due to the subsequent drying by heat and other influences. Coloring of the compound granules by addition of dyestuffs to the polymers during the extrusion operation, however, leads to reproducible results.

It is known per se to the person skilled in the art that the leather pellets produced from the ground leather stock as a rule cannot withstand exposure to heat at temperatures above 180 °C because of natural denaturing and, in the presence of oxygen, tend to burn and/or release combustion odors. On the other hand, there is a need for compound granules which can also withstand higher temperatures.

Experiments have shown that, surprisingly, thermoplastic polymer materials having a melting temperature above 180 °C can also be used in the production of the compound granules. In order to be able to employ thermoplastic polymer materials of this type, it is proposed according to the invention that the polymer material formed as a thermoplastic is heated in the molten or softened state to a temperature above 180 °C, and that the cold or preheated leather pellets are added to the heated polymer material and mixed with this, while cooling the mixture, before the finished mixture is shaped to form the granules.

In a preferred embodiment of the method according to the invention, the polymer material is heated along a heating zone of an extruder to a peak temperature above 180 °C, while melting or softening, the leather pellets are admixed in the cold or preheated state to the polymer material downstream of the heating zone and the finished mixture produced in this way is discharged via an exit die or a die plate at a temperature which is lowered with respect to the heating zone, and is shaped into the compound granules. A thermoplastic polymer material with a melting or softening point above 180 °C, preferably above 220 °C, is advantageously used for this.

The compound granules produced in this way are a further intermediate product. It comprises granules of a thermoplastic and leather fibers, in which the thermoplastic has a softening point above 150 °C, preferably above 180 °C.

According to the invention, the compound granules as the intermediate product are preferably used for producing moulded parts by means of an injection moulding process. Experiments have shown that the compound granules in principle can also be heated to temperatures above 180 °C in the injection moulding machine before they are injected into the cavity of the injection moulding machine. The relatively high heat stability is presumably to be attributed to the fact that the leather fibers within the compound granules are surrounded by a protective layer which counteracts denaturing of the leather fibers. In addition, the oxygen, which would promote combustion of the leather fibers, is displaced or shielded by the polymer material. An improvement in this respect can also be achieved by a suitable process procedure in which the dwell time in a heating zone of the injection moulding machine is minimized.

Moulded parts can be produced from the compound granules by means of the injection moulding process. Due to the leather content, such moulded parts have optical and haptic properties of leather, which make a use for producing moulded parts, such as hand grips for tools, Nordic walking sticks, bicycle handlebars, grips on sports equipment and many others of the like, particularly advantageous. This method is likewise particularly suitable for sheathing vehicle steering wheel rims. For such uses where the grip friendliness of leather material was desired, an expensive application of genuine leather hitherto had to be effected. The procedure according to the invention provides an inexpensive and therefore widely applicable alternative here. The compound granules according to the invention are likewise suitable for producing moulded parts such as toy figures, since optical and haptic properties which make the figures look more realistic also arise here.

The compound granules are moreover suitable for producing films by calendering. Such films can be employed in all instances where films purely of plastic or genuine leather have hitherto been used.

The invention is explained in more detail in the following with the aid of the drawing. The figures show

Fig. 1 a block diagram for a method for producing leather pellets, compound granules and injection moulded parts using shavings obtained in leather production;

Fig. 2 a section through an extruder for producing compound granules;

Fig. 3 a section through an injection moulding machine for producing injection moulded parts using compound granules as an intermediate product.

On the basis of the block diagram according to Fig. 1, the shavings obtained in leather production, which have an initial moisture content of 15 - 60 wt.%, are introduced via a feeding station 10 into a fine mill 12 and ground there to a fiber or particle size of approx. 0.5 mm. After this process step, the shavings can optionally be colored in a universal mixer 14 by addition of a dyestuff. After the grinding, the material has a moisture content of about 15 - 50 wt.%. The ground shavings are now pressed in a press 16 to give leather pellets. During this procedure, the moisture content decreases further to about 10 - 40 wt.%. If necessary, this can be followed by a drying operation in a drier 18, until the leather pellets have a residual moisture content of < 9 wt.%. The leather pellets produced in this way are transferred as bulk goods into a drum of any desired size. The storage life of such leather pellets is months to years, so that immediate further processing is not necessary.

For further processing, the leather pellets can be further processed to compound granules in plants specifically equipped for this, so-called compounders. For this, the leather pellets are mixed and extruded with a thermoplastic polymer material in an extruder 20 corresponding to Fig. 2. During the extrusion, the polymer material, which is conventionally present as granules, and the leather pellets are led together along a mixing and conveying zone within the extruder by means of conveying screws 22 under the action of pressure and heat. The polymer material fed into the intake zone 24 in the form of granules is first heated along several heating zones 26, and thereby melted. The leather pellets are fed in downstream of the intake zone 24 via a side feed 28 and admixed with the molten polymer material. The compounding takes place along the further conveying zone 30. The leather pellets are finely ground there, so that the extrusion product has an approximately homogeneous distribution of leather fibers in a matrix of plastic. Excess moisture is removed from the melt via the devolatilization opening 32 by means of a vacuum pump. The material mixture ejected in the form of a strand from the extruder 20 through a die plate 34 is in its turn cut off in the desired length and forms the compound granules as the process product. A dyestuff which determines the color of the compound granules and of the moulded parts or films subsequently produced therefrom can be added to the polymer material if this has not already been colored beforehand.

Possible thermoplastic polymer materials are, preferably, polypropylene, polyethylene or thermoplastic elastomers. It has been found that those polymer materials having a melting temperature above 180 °C can also be used in a suitable process procedure. This is surprising inasmuch as according to conventional knowledge, the maximum temperature to which leather can be exposed is about 180 °C.

The compound granules produced in this way can in turn be transferred into drums of any desired size and delivered to the end processor, for example the injection moulding plant or the film manufacturer.

Processing of the compound granules to moulded parts by means of an injection moulding process is particularly advantageous, the moulded parts produced in this way having optical and haptic properties typical of leather. For this purpose, with an injection moulding machine 40 according to Fig. 3, the compound granules are fed via a hopper 42 and an intake 44 to an injection unit 46 in which the granules are ground along a conveying zone 48 by means of a screw 50, heated to the melting temperature in several heating zones 52 and injected via a nozzle 54 into an injection mould 56. The cavity 58 of the injection mould 56 determines the shape and the surface structure of the finished moulded part.

Mass products can be produced with a high accuracy in a short time by the injection moulding. In this context, the surface of the component can be virtually freely chosen. Smooth surfaces, grain for contact-friendly areas, patterns and engravings can be introduced in the course of the production operation. Parts which are to meet decorative requirements or are intended for manual use, such as grips for tools, tennis racquets, Nordic walking sticks, steering wheel rims for vehicles and the like, are possible for the leather-plastic compound.

On the other hand, the compound granules can be processed by calendering, in which molten compound granules are led through as a rule several successive heated roll nips and thereby brought to the desired thickness, to give films with a use spectrum which covers that of conventional films of plastic.

Summarizing, the following is to be said: The invention relates to a method for producing leather pellets, a method for producing compound granules of leather pellets and a polymer material and the use of such compound granules for producing moulded parts or films. The leather pellets are produced by the following steps: Shavings are obtained as waste products in leather production; the shavings are comminuted to a ground leather stock containing leather fibers; the comminuted stock is pressed to leather pellets; and the leather pellets are dried to a residual moisture content of a maximum of 30 wt.%. The leather pellets can be mixed with a polymer material in a ratio of 10 - 95 wt.% and bonded to one another to form compound granules as a further intermediate product, and shaped. These compound granules can be used for producing moulded parts by means of injection moulding or films by means of calendering.

List of reference symbols: 10 Feeding station 12 Fine mill 14 Universal mixer 16 Press 18 Drier 20 Extruder 22 Conveying screw 24 Intake zone 26 Heating zones 28 Side feed 30 Conveying zone 32 Devolatilization opening 34 Die plate 40 Injection moulding machine 42 Hopper 44 Intake 46 Injection unit 48 Conveying zone 50 Screw 52 Heating zones 54 Nozzle 56 Injection mould 58 Cavity

Claims

1. A process for the manufacture of leather pellets, in which: - chips are extracted as waste products in the manufacture of leather, - chips are reduced to a leather grinding material containing leather fibers, characterized in that - the chips have an initial moisture content of 15-60% by weight, - pressed into leather pellets - the said pellets are dried until they have a residual moisture content of max. 30% by weight.

Process according to claim 1, characterized in that the chips are recovered by a chrome tanning or tanning with glutardialdehyde.

Process according to one of Claims 1 or 2, characterized in that the chips or finished leather waste products are reduced to a fiber or grain size of approx. 0.5 mm.

Process according to one of Claims 1 to 3, characterized in that powdery dye is added to the leather grinding material in a blender.

Process according to one of claims 1 to 4, characterized in that said leather pellets are dried at a temperature of up to 110 ° C until they have a residual moisture content of <9% by weight.

Process according to one of Claims 1 to 5, characterized in that said leather pellets are mixed with a polymeric material in the ratio of 10-95 wt.% And pulverized and together to form a compound granulate and bonded together and formed.

Process according to claim 6, characterized in that a dye is added to the polymer material before mixing with said leather pellets.

Method according to claim 6 or 7, characterized in that the mixture of leather pellets and polymer material is extruded into the compound granulate in an extrusion machine.

Process according to one of claims 6 to 8, characterized in that the polymeric material formed as a thermoplastic is heated in a molten or softened state to a temperature above 150 ° C and that the said leather pellets in cold or preheated state are added to the heated polymeric material and mixed with it while cooling the mixture before forming to form the granulate.

Process according to claim 9, characterized in that the thermoplastic polymer material is heated to a temperature above 180 ° C, preferably above 220 ° C, before the said pellets are added to the heated polymer material.

Process according to one of claims 6 to 10, characterized in that the polymeric material consisting of a thermoplastic material is heated along a heating stretch of an extruder to a temperature above 180 ° C, preferably 220 ° C during melting or softening. said cold or preheated leather pellets are blended into the polymeric material upstream of the heating stretch and that the compound mixture thus produced is poured out via an outlet nozzle and formed into the compound granulate.

Process according to one of claims 9 to 11, characterized in that a thermoplastic polymer material having a melting or softening point of more than 180 ° C, preferably above 220 ° C, is used.

Use of the compound granulate according to one of claims 6 to 12 for the manufacture of mold parts by means of an injection molding method.

Use according to claim 13, characterized in that the compound granulate is heated in an injection molding machine to a temperature above 180 ° C before being injected into an injection mold.

Use of the compound granulate according to one of claims 6 to 12 for the production of foils by a calendering method.

Use according to claim 15, characterized in that the compound granulate is heated to a temperature above 180 ° C before being fed to a calender stretch.